ROME – George Clooney stoked an age-old point of friction between Italy and France this week when he commented that the Mona Lisa, the centerpiece of the Louvre museums in Paris, should be returned to Italy.

Clooney was in Italy as part of a promotional tour for The Monuments Men, the World War II-era film about a group of experts conscripted to help save artistic treasures from destruction at the hands of the Nazis.

Joined on his stop in Italy by co-stars Matt Damon, Bill Murray, Bob Balaban, Jean Dujardin, and John Goodman, the 52-year-old filmmaker -- who co-wrote, co-produced, directed and starred in the film -- raised the most eyebrows when he said the 500-year-old masterpiece painted by Tuscany native Leonardo da Vinci should be returned to its country of origin.

The Monuments Men cast posed for a photo in Milan in front of another da Vinci masterpiece, The Last Supper. Even that caused some controversy, as rules prohibit photos or bright light in that chamber because the fresco is fragile.

The Mona Lisa, considered the world's most famous painting, was acquired by French King Francis I shortly after it was completed, approximately around 1518. It has hung in the Louvre since 1797. Several times in the past, Italy has mounted a challenge to request the famed portrait of Florentine noblewoman Lisa Gherardini be returned, either permanently or temporarily.

The last time was in 2012, when the Italian Ministry of Culture and the Province of Florence collected more than 150,000 signatures in an appeal to the Louvre to have the masterpiece loaned to Florence's Uffizi Gallery for the 100th anniversary of the recovery of the painting. The painting had been stolen in 1911 by Italian Vincenzo Peruggia, who sought to return the piece to Italy. It was recovered in a Florence hotel room in 1913, and afterwards it was displayed briefly in Florence and Rome -- the last time the painting was displayed in Italy.

The Louvre declined that request -- at least in part because of fears Italy might not return the painting, though the official reason was that museum officials believed the painting is too fragile to travel.

Clooney's remarks have reopened the debate and sparked new calls from some corners for the Mona Lisa to be returned to Italy. But so far, France has refused to budge on the issue.

Clooney's remarks were part of a wider call for works of art to be returned to their countries of origin. While at the Berlin Film Festival, for example, Clooney and Murray called for the repatriation of the 2,500-year-old Parthenon Marbles, a set of sculptures that were taken from Greece by Thomas Bruce, the 7th Earl of Elgin, who brought them to England 200 years ago.